1. Field of the Invention
The present invention generally relates to a matrix switch board and a connection pin, and more particularly, to a matrix switch board and a connection pin which are used in a main distributing frame (MDF) having a function of flexibly changing a connection between a subscriber and a switching system.
The present invention further is directed to a matrix switch board unit having a plurality of the matrix switch boards, and a method of fabricating the matrix switch board and the connection pin.
2. Description of the Related Art
FIG. 1 shows an illustration for explaining a typical function of a main distributing frame (MDF). The MDF is equipment for flexibly connecting a plurality of subscriber-side terminals and subscriber circuits located in a switching system. In the MDF, when a new subscriber is applied, the new subscriber is connected with the switching system, and when an address or a telephone number of the subscriber is changed, the connection between the subscriber and the switching system is changed. The connection changing may be carried out during an operation of the switching system. For efficient connection changing, the number of subscriber-side terminals (for example, X=3600 terminals) provided in the MDF is commonly larger than that of switching-system-side terminals (for example, Y=2100 terminals).
In the conventional MDF, as shown in FIG. 1, two terminal boards are provided. The subscriber and one terminal board are connected by a pair of cables, and the other terminal board and the switching system are also connected by a pair of cables. Further, the above two terminal boards are manually connected by a maintenance man using jumper wires to connect the subscriber and the switching system. Therefore, for the above-discussed connection work, a specially-skilled engineer is required. There is thus a problem that when the MDF is located in a remote area or an unmanned exchange office of an isolated island, it takes a long time to send the maintenance man, and, as a result, the connection work for a variety of services, for example, telephone service, may not quickly be carried out. Further, since the above connection work is carried out mainly during the operation of the switching system, errorless work is required. Accordingly, it takes a long time for that connection work. To overcome these problems, recently, an automatic MDF has been developed, wherein the jumpering work is carried out by a robot.
FIG. 2 to FIG. 4 show a configuration example of a prior-art automatic MDF. FIG. 2 shows a principle of the prior-art automatic MDF. FIG. 3A to FIG. 3C show configurations of prior-art matrix switch board and connection pin used in the prior-art automatic MDF. More specifically, FIG. 3A shows the configuration of the prior-art matrix switch board, FIG. 3B shows the configuration of the prior-art connection pin, and FIG. 3C shows an illustration indicating a condition in which the connection pin is inserted into the matrix switch board. FIG. 4 shows a configuration of the prior-art automatic MDF.
As shown in FIG. 2, in the prior-art automatic MDF, instead of the terminal board for the jumpering, a matrix switch board (MB) is provided. The matrix switch board is constructed with a multilayer-structure-type board, wherein a plurality of subscriber-side wires X and a plurality of switching-system-side wires Y are arranged in different layers so that the wires X, Y cross at substantially a right angle. At each cross point, a cross-point hole is provided in the board, wherein by inserting a connection pin into the cross-point hole, a desired subscriber-side wire X can be connected to a desired switching-system-side wire Y. In the automatic MDF, an inserting operation of the connection pin is automatically carried out by a robot.
When, for example, in one matrix switch board, 3600 terminals on the subscriber side and 2100 terminals on the switching system side are provided, 7.50-million cross-point holes need to be provided. In this case, robot control is subjected to a large amount of load. Therefore, in practical use, by arranging a plurality of small-sized matrix switch boards in a network-structure formation based on a given rule, substantially the same function is realized. In this method, the number of the cross-point holes may be extremely reduced.
Such a matrix switch board, as shown in FIG. 3A and FIG. 3C, is constructed with a printed wiring board having 4 conductive layers. In general, a connection between the subscriber and the switching system is wired by A-line wires and B-line wires, and for high efficiency, the two wires of each type are simultaneously connected. Therefore, the prior-art matrix switch board has the subscriber-side wires provided with two layers (the A-line X layer and B-line X layer) and the switching-system-side wires provided with two layers (the A-line Y layer and B-line Y layer), wherein the two groups of wires cross at substantially a right angle. At each cross point of these wires, a hole penetrating the printed wiring board is provided. In the prior-art matrix switch board, an interval of a distance between adjacent holes in the printed wiring board is approximately 1.5 mm.
The prior-art connection pin has, as shown in FIG. 3B, two cylindrical connection springs a, b arranged in series in an axial direction. By inserting the connection pin into the cross-point hole of the matrix switch board, as shown in FIG. 3C, both connections between the subscriber-side A line and the switching-system-side A line and between the subscriber-side B line and the switching-system-side B line can simultaneously be wired. The prior-art connection pin has approximately an 8.7-mm length and is approximately 1.2 mm in diameter.
In the prior-art automatic MDF, as shown in FIG. 4, a plurality of matrix switch boards 1 is dimensionally arranged so as to form one flat board. Two such flat boards are arranged on both sides of an apparatus 4 accommodating a robot 3 for inserting a connection pin 2. The robot 3 searches for a designated cross-point hole 5 in the flat board, and inserts the connection pin 2 into the cross-point hole 5. The connection pin 2 mounted in the robot 3 can turn in an opposite-side direction, and can also be inserted into the matrix switch board of the flat board arranged on the opposite side. Because the connection between the subscriber-side line and the switching-system-side line is carried out mainly during the operation of the switching system, one connection pin 2 is inserted for one transmission line to be connected. Since in the above-mentioned automatic MDF, a plurality of the matrix switch boards is dimensionally arranged, a width of the flat board may be several meters.
However, the above-mentioned prior-art matrix switch board and connection pin have the following disadvantages.
The matrix switch board requires a large number of cross-point holes. However, the number of cross-point holes which are practically used is a part of the total number. Namely, most of the cross-point holes may not be used, but are required for small probability of use. Therefore, for the automatic MDF, reduction of cost for one cross-point hole of the matrix switch board is one of important themes.
Accordingly, in the prior-art matrix switch board, reduction of an arranging pitch and a diameter of the cross-point hole, and reduction of the diameter of the connection pin have been tried. However, for the above-mentioned processes, manufacture precision for a fine structure requires further improvement, and this requirement obstructs cost reduction.
Further, when the wiring patterns for the communication lines are arranged close to each other, a cross talk commonly occurs, wherein a signal transmitted in one communication line leaks to another communication line as noise. In the prior-art four-layer structure matrix switch board shown in FIG. 3A, since the pair of wiring patterns in the subscriber side are simultaneously connected with the pair of wiring patterns in the switching-system side by one connection pin, the pair of wiring patterns in the subscriber side and the pair of wiring patterns in the switching-system side are subsequently arranged in a vertical direction. In such a wiring-pattern structure, there is a problem in that it is difficult to reduce the cross talk between the communication lines provided by the wiring patterns.
Furthermore, the prior-art connection pin needs to have two connection parts. Therefore, it is necessary to fix ring-type connection members to a plastic rod while maintaining a good joint property. Therefore, there is thus a problem in that assembling the connection pin is difficult, and, thus, the cost of the connection pin increases.